Resistance and Aerobic Exercise for Prevention in Women With Dense Breasts (REP-D)

This study is investigating whether resistance and aerobic exercise can reduce breast density in women with dense breast tissue. Dense breasts are a risk factor for breast cancer, and researchers want to find out if exercise can lower that risk by reducing breast density over time. **You may be eligible if:** - You are a woman between 18 and 59 years old - Your most recent mammogram showed heterogeneously dense or extremely dense breast tissue (BIRADS category 3 or 4) - You currently exercise less than 60 minutes per week at moderate or vigorous intensity - You are not pregnant or breastfeeding - You can read and speak English **You may NOT be eligible if:** - You are unable to walk two blocks at any pace - You have a history of breast cancer - You have physical limitations that prevent exercise participation - You are pregnant or currently breastfeeding Talk to your doctor to see if this trial is right for you.